1. Technical Field
The present invention relates to a color conversion method, a color conversion table created by the color conversion method, an image processing apparatus, and a color conversion program. More specifically, the invention relates to a color conversion method for converting first color data in a first color space to second color data in a second color space, based on a first profile that defines the correspondence between the first color space that is expressed by a first chromatic color and a first black and a predetermined device-independent color space, a second profile that defines the correspondence between the second color space that is expressed by a second chromatic color and a second black and the device-independent color space, and a color conversion rule in the device-independent color space, a color conversion table created by the color conversion method, an image processing apparatus, and a color conversion program.
2. Related Art
In the related art, when performing color matching between image data of one color space and image data of another color space, if the one color space is expressed by composite colors (for example, CMY components) and black (K) and another color space is expressed by composite colors (for example, CMY components) and black (K), there is reported a phenomenon that K=0 is converted to K≠0 or K≠0 is converted to K=0. Such a phenomenon is reportedly attributed to conversion of K to black expressed by equal CMY quantities or conversion of black expressed by equal CMY quantities to K or the user's tone curve adjustment.
In order to address such a phenomenon, a full-black method, clipping of K values, and the like have been proposed (for example, see JP-2003-324623). Moreover, calculation of K considering the color reproducibility has been proposed (for example, see JP-B-4022748).
The full-black method is a simple method of substituting a color expressed by equal CMY quantities (C=M=Y) with K. Although this method takes tinge into consideration to some extent, since the characteristics of each device are not taken into consideration, a change in tinge is noticed. Moreover, the blacks originally produced by the equal CMY quantities are all substituted with black, the granularity increases and thus a resulting image is printed with whiskers being observed on a face or the like.
When the K values are clipped (that is, an input of K=0 is output as K=0 and an input of K≠0 is output as K≠0), it is unable to take color matching into consideration, greatly changing the black quantity, and thus the tinge is greatly changed. Therefore, the full-black method or the clipping of K values is not appropriate.
In the calculation of K values considering the color reproducibility, a tone distortion or the like is not likely to occur since the K values at which mapping does not occur are calculated considering a gamut area. However, in a system allowing a user to control the color reproduction, since it is not allowed to place limitations on the gamut area, the clipping occurs if the K values to be processed are outside the gamut, and thus the tone distortion occurs.